Generally, a gauge capable of indicating the level of fuel stored in a fuel tank is provided on an instrument panel positioned in front of a driver's seat of a vehicle, and a sender unit capable of sensing the level of the fuel is installed in the fuel tank, so that a signal corresponding to the level of the fuel sensed by the sender unit can be transmitted to the gauge to inform the level of the fuel remaining in the fuel tank.
FIG. 1 is a view showing a conventional device for sensing the level of remaining fuel, which is installed in a fuel tank of a vehicle. A sender unit 10, and a casing 11 of the sender unit 10, is fixed to a guide member 2 fixed to an upper end of the interior of a fuel tank 1, and has a pivotable wire arm 21 with a float 20 fixed to one end thereof.
The float 20 moves upward or downward by its buoyancy depending on the level of the fuel, and the upward or downward movement of the float 20 is converted into a rotational movement of the wire arm 21.
Meanwhile, in the sender unit 10 to which the wire arm 21 is pivotably coupled through a hinge is provided a variable resistor of which the resistance value varies depending on the rotation of the wire arm 21. Depending on variations in the resistance value of the variable resistor, a signal is transmitted to a fuel gauge on the instrument panel to indicate the level of fuel remaining in the fuel tank.
As described above, the conventional sender unit that is a contact type using the variable resistor has been widely used. In addition to such a contact type sender unit, there are non-contact type sender units such as those using a Hall element, a magnetic force type, and an encoding type with an encryption plate.
However, in the contact type sender unit described above, the operation for sensing the level of fuel is performed by means of rotation of the wire arm connected to a movable contact which is brought into electrical contact with a resistance track formed on a PCB or ceramic substrate.
That is, since the level of fuel is detected depending on the degree of relative rotation of the movable contact on the resistance track in the conventional contact type sender unit, there are many problems associated with deterioration of a durable lifetime and linearity of an output value due to brush abrasion or poor resistance, i.e., limitations on the accuracy of measurement, and the like.
On the other hand, the non-contact type sender unit has superior properties in view of durability and accuracy contrary to the contact type sender unit. However, there are problems in that precise processing operations are required and manufacturing costs are high. Specifically, in case of a non-contact type magnetic position sensor, there is considerable difficulty in manufacturing it in a smaller size, and there is a problem in that an operation for laminating silicon steel sheets, which are used for reducing loss due to an eddy current, should be involved, resulting in reduced processing efficiency.